Continuous process for leaching an iron-aluminum alloy



R. C. MCMASTER Aug. 26, 1952 CONTINUOUS PROCESS FOR LEACHING AN IRON-ALUMINUM ALLOY Filed June 19, 1947 M. A Af Krfvc @f5 @ivi @www if 2727572752 `/fPoesE/Pr 6 Nef/Anm columnv relatively cool. ivigorouslylupon coming into contact with thelhot patented ug. 26, 1.952

UNITED STAT CONTINUOUS PROCESS FOR LEAGHING N IRON-ALUMINUM ALLOY Robert C. McMaster, Columbus, Ohio, assigner, by mesne assignments, to The IndianaSteel Products Company, Valparaiso, Ind., a corporation of Indiana Application June 19, 1947, serialNo. 755,751' I This invention relates to a continuous leaching process, and more particularly to a continuous process for the leaching of iron-aluminum alloys to produce a iinely divided residue having permanent magnet properties and consisting largely of well dispersed, iinely divided FegO/i in a matrix of oxyferrite,

In order to develop the highest possible magnetic properties in the material prepared in leaching iron-aluminum alloys, I have found it desirable to limit the time of contact between the particles of the iron-aluminum alloy and the Aleachant, which is preferably an aqueous solution of a caustic alkali, such as sodium hydroxide. u The control of contact time to a minimum canl best be accomplished in a continuous process in: whichl theiinely divided particles of the ironaluminum alloy `are charged into the top of a vertical `column of the leachant and maintaining the top portion of the column at or near its boiling point, while keeping the lower part of the The alloy particles react lea-chantlbut when the reaction has gone to completion, the particles fall by gravity through the hot portion of the column into the relatively cool caustic alkali solution.v Since there is an evolu- .tion of hydrogen from the reaction between the alloy particles :andthehot caustic alkali solution, thereis a` tendency of the alloy particles to be buoyed up until the completion of the reaction. Consequently, each .alloy particle, independently of its size within certain limits, remains in the hotleachant until the completion ofthe reaction and then automatically falls by gravity into the relatively cold `portion of the column. In this way, the time of contact with the hot leachant is limited to that required for complete reaction.

vThe leaching reaction is complete when the leached particles enter the cold caustic solution 'zona Due to the lack of gas evolution in this cold.zone, the leached particles pass through the zone without substantial hinderance.

From the relatively cool lower portion of the `column, lthe leached alloy particles are `either continuously or periodically transferred into a countercurrent Washing system. The washing removes substantially all of the water solubleV products of `reaction `which in the case of iron- 4 Claims. (Cl. 213-4200) toV during the leaching operation. Inthis way oxidation and loss of magnetic properties of the leached product is avoided. From the washing system, the washed, leached particles are collected for further processing in the manufacture of permanent magnet material from such. particles.

It is therefore an important object of this invention to provide a continuous leaching process wherein the time of leaching is automatically regulated in accordance with the time required` for completion of the reaction that occurs between the particles to be leached and the leachant.

It is a further important object of this invention to provide a process for `the continuous leaching of iron-aluminum alloys by means of aqueous caustic alkali solutions, wherein the alloy in finely divided particle form is rstintroduced into the upper, heated portion of a column of the leachvention will be apparent from the disolosuresin the specification and the accompanying drawings.

On the drawings, the figure is a vertical `sectional view, partly in elevation, ofapiiaratusisuitable for carrying out thep'rocessof my invention.

The reference numeral lil indicates anfl'ngated cylindrical vessel arranged verticallyfor conning a column of leachant, indicated at Il.

,The vessel l0 may be open atboth ends and.` provided at its 'lower end with an apertured closure member I2, into which is inserted the upper end of a second, relatively smaller diameter cylindrical vessel I3.` A gravity acting valve M serves `to close the upper end I5 of the lower cylindrical vessel I3 and thus also close the lower end of the upper cylindrical vessel Ill.` A stem I6 extends from the valve I4 to a point above the upper end of the upper vessel l0, where a loop I1 is provided for manual manipulationofs'aid valve 4.

The upper vessel I 0 is provided intermediate its height with means, indicated generally at` IB, for heating the leachant in the portion of the column indicated at A.` Said means Hl: may ,suitably comprise an electric heatenthe coils I9 4'of which are wound around the vesselJtl and are connected through a rheostat 2,0 withfpower lines 55.,`

columnV at a relatively low temperature, coldA leachant is introduced into Vthe bottom of said Y rent, such as A. C. at 110 volts. When the heater vessel IIJ, as at 23, through a tube 24 connected to a reservoir 25 and provided with a petcock 28 for the regulation of ow of leachant into said lower portion B of the column. The rate of flow is so regulated as to maintain the heightV of the column of leachant in the vessel I substantially constant. A tube 21 inserted into the side wall of the vessel I8 just above the heating unit I8 serves te dra'w olf spent leachant at a rate proportional to the rate of consumption of theV active 4ingredients in the leachant. lSaid tube v21 is providedwith an upwardly oilset portion 28 to retard the'passage of Vparticles of the alloy along with the spent leachant. As a further means of preventing excessive loss of alloy particles through the side drain 21, an electromagnet 29 is positioned onV the opposite wall of said vessel I0 to `attract the magnetic particles away from the "opening into the side tube 21. The spent leachant passing through the side tube 21 discharges into avessel 30. Y

The lower cylindrical vessel I3 serves for the washing of lthe leached particles and for this purposeis provided with a Water intake 3l near l thebottomn thereof and a water outlet 32 near the top thereof. v

The lower end of the cylindrical vessel I3 is 'provided witha plug 33 and a valved outlet therethrough 34,7 through which the leached and washed -particles may lbe withdrawn from the system. When the valve I4 is lifted from the upper end`l'5 of the vessel I3 leached particles are dischargedinto said lower vessel I3 for counterj'current washing byV means of the upward flowing ,stream of water introduced through the inlet 3 I.

#In order to assist the washing operation, electromagnets, indicated at 35, 3 6 and 31, may be posi- 'tionedalong the wall of the vessel I3 to effect Amagnetic agitation of the particles as they fall downwardly through said vessel I3. In this way "much of the water soluble products of reaction is removed from the leached particles as they fall l*through the upwardly ilowing stream of water in v'thejvessel I3.

' The head of water maintainedv in the vessel I3 iscontr'olled by means of a vertically adjustable Ytube 38 connected to the outlet tube 32 and providedwith an overflow 39 near its upper end.

By adjusting the vertical height of the tube 38, "the-pressure head on the column of water in the vessel I3 maybe controlled so as to prevent subiwasliing effect on the particles as they proceed downwardly toward the dischargeoutlet 34.

' The process will now be described in connection with the leaching of an ironV-aluminlun alloy.

v1t will be understood, however, that the principle's of my invention are equally-v applicable to 'other problems of leaching.

,Y A; causucgjalkall solution, which may suitably like "an aqueous solution Vof caustic "soda of Y% eondehtiatoby w'e'ighhis VVintrddlled into the solution through the inlet 24.

1Vof the reaction 4 vessel IU to the level of the side tube `21. The heater I8 is then energized to heat up the solution in the portion A of the column to a temperature near the boiling point of the solution, which in this case will be around 110 C. 4When this' temperature is reached, the valve I4 being closed, of course, throughout this operation, finely divided particles of the iron-aluminum alloy are introduced from a valve controlled funnel 40 containing4 a supply 4I of said particles into the upper open end of the vessel IU at a suitable rate. This rate, in general, should be proportional vto the rate of introduction of the fresh caustic soda The optimum proportion has been found to be about one part of alloy particles to 20 parts of caustic soda solution of around.3.0% concentration, by lweight.

The particle size of the alloy should be Afiner than 40 mesh and preferably such as to pass through a V mesh screen. The caustic soda solution should Vbe between 10` andv40% concentration and preferably 30% by weight. y The iron-aluminum alloy powder introduced at the top of the chamber reacts vigorouslywhen it reaches the hot caustic soda solution. Due "tov the rapid levolution of hydrogen as 'a result Tof such reaction, a great deal of frothing occurs'jand this froth, or foam, substantially fills the vessel above the liquid level therein, whichis controlled by the height of the sidev tube 21. The froth comparatively stationary and so light as not to increase appreciably the head above the side tube connection to the vessel I0. The rate 'o'fintroduction of cold caustic soda solution Vinto 'the vessel ID is such that the overflow out through the side tube 21 is at a sufciently low 'enough linear velocity to avoid carrying particles uppast then upwardly, Voffset portion 28.

vBecause of the rapid formation of gas bubbles during 'the active leaching of the particles, and the tendency of the bubbles to lclingto the .'reacting particles until the Vparticles riseto the `top surface of the leaching solution, the rapidly leaching particles remain in the `reactionzone A of the vessel until leaching is substantiallycompleted. Y As the leaching reaction continues, the

more fully Areacted particles tend to dropdowniwardly .from the upper surface Yof the leachant, `trailing bubblesof gas as they sink, butusua'lly developing renewed activityand rising again .to

vthe surface several times before the Yreaction slows B of the column is'maintain'ed at a relativelybeoi temperature, say, not above 60 C, andprefel 'ably around room temperature.. VIf this caririigt'f;V accomplished by the rate of infiow'ofcold soda from vthe reservoir 25 "through the tu l24', the lower portion of the-vessel IU may be pro with a water jacket for cooling purposes.

`leached particles drop from the reaction zone: A

into the lower chamber B, the leaching Vreaction ls abruptly ended, but at "thl's'polnp the reaction is Substantially complte due to the buoyant 'effect of the gas bubbles in' zo'neA.V Thus, -the'ti'm'e'of leaching 'is automatically] controlled by there- 'actionitselil the leached particles dropping"*out zone' Vas soon "as thereactioilV is complete.

As 4the leached particlesr pass downwardly through `the cold NaOI-I solution, theisodium aluminate produced by the leaching reaction is largely dissolved away fromthe particlesby the caustic soda solution.` Since the particles are widely separated from each other as they pass through this washing zone, they are each washed thoroughly ina copious supply of caustic-soda Washing solution, yet are in contact with `that solution onlya very limited time, of theorder of 5to 30seconds. j ,i i

f By means of the apparatus disclosed, the .temperature of the solution in the lower portion ,B of .the4 column may be kept.below 6.0 C. `while `the ternperaturefin,the` upper partA is maintained at its:` boilingpoint. Inthis sway a minimum amount of mixing occurs between the solutions in the two portionsof thecolumn'.

y Aslleached particles reach the bottom of the vessel I0, the valveld is lifted to' discharge these particles into the lower vessel I3. While the valve I4 is lifted, the pressure adjusting tube 38 is lowered sufficiently to reduce any tendency of the Water to flow upwardly through the upper end I5 of the vessel I3' and to permit the leached particles to proceed downwardly into the lower vessel I3. In the column I3, the particles are subjected to countercurrent washing with water to remove adhering soluble products of the reaction, such as sodium aluminate. and also such caustic soda as enters the upper end I5 of the vessel I3 along with the leached particles, The electromagnets 35, 36 and 31, may be operated if desired to magnetically agitate the particles falling through the vessel I3. i i

By the continuous leaching process as herein described, the alloy particles are each leached under identical conditions. This maintenance of constant conditions results in the production of a product having consistent properties not obtainable by former batch operations.

The fully washed particles are removed either continuously or periodically from the bottom of the vessel I3 through the valve controlled outlet 34. These particles may then be further processed as disclosed in the pending Howell application Serial No. 731,721, filed February 28, 1947, assigned to a common assignee.

As there described, the residue from the leaching and Washing steps consists largely of FeaO4 in a matrix of oxyferrite. Such residue has very desirable magnetic properties that are possessed to a degree not found in the ordinary magnetic oxides of iron. While my process has been described in connection with the leaching of iron-aluminum alloys, it is equally applicable to the leaching of aluminum alloys of other heavy metals, such as nickel and cobalt, and to the leaching of other metallic alloys generally.

It will, ofcourse, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. A continuous process for the leaching of an iron-aluminum alloy, which comprises introducing nnely comminuted particles of said alloy into an aqueous caustic alkali solution, maintaining the solution in the upper part of said column at near its boiling temperature during introduction of said alloy, introducing a cold fresh aqueous caustic alkali solutiorrnear the Lbottomzoffsaid columnl withdrawing `spent caustic :alkali '.solu-Y tion near the top :of said column, controlling the inflow of fresh caustic alkali solution at sucha rate as to maintain the lower part. of .said colf. umn-relatively cool with respect to'the upper part of said column but not at a sufliciently rapid rate` to cause particles present inV said upper part Vto pass outwith the spent caustic alkali solufA tion and intermittently releasing the leached particles from the bottom of the caustic alkali solution` column `intothe top of` ,an upwardly flowing column of wash water.

2. A continuousl process for'the leaching of an ironfaluminum alloy, which Acon'lprises introducing inely comminuted particlespf saidfalloy intoV a column of an aqueous caustic alkali. solution equivalent to about 30% sodiumhydroxide concentration, maintaining the solution in the` upper part of. said column at near `its boiling tempera"- ture during introduction of said alloy. introducing a cold fresh aqueous caustic alkali solution of similar concentration near the bottom of said column and withdrawing spent aqueous caustic alkali solution near the top of said col-umn, the weight of the fresh solution introduced being about twenty times the weight of the alloy introduced in the same period of time, controlling the inflow of fresh caustic alkali solution at such a rate as to maintain the lower part of said column relatively cool with respect to the upper part of said column but not at a sufficiently rapid rate to cause particles present in said upper part to pass out with the spent caustic alkali solution. and intermittently releasing the leached particles from the bottom of the caustic alkali solution column into the top of an upwardly flowing column of Wash water.

3. A continuous process for leaching of an alloy of aluminum in a ferromagnetic metal, which comprises charging the alloy in particle form into the top of a column of an aqueous caustic alkali solution, maintaining the solution near thevtop of the column suiliciently hot to leach particles charged thereinto, the hot caustic alkali solution reacting with the aluminum of the alloy to evolve hydrogen and the buoyant eifect of the hydrogen gas so evolved serving to maintain the particles in the top of the column during the leaching of the particles, introducing a cold fresh aqueous caustic alkali solution near the bottom of said column and withdrawing spent aqueous solution near the top of said column, controlling the inflow of such fresh caustic alkali solution at such a rate as to maintain the lower part of said column relatively cool with respect to the upper part of said column but not at a suii'iciently rapid rate to cause particles present in said upper part to pass out with the spent caustic alkali solution, and intermittently releasing the leached particles from the bottom of the caustic alkali solution column into the top of an upwardly ilowing column of wash water.

4. A continuous process for the leaching of an alloy of aluminum and a ferromagnetic metal, which comprises subjecting the alloy in particle form to the action of a hot aqueous alkali solution with resultant evolution of hydrogen gas. the liberation of such gas during the leaching operation maintaining said particles in contact with the hot alkali solution until leaching of the particles is substantially complete, introducing a cold fresh caustic alkali solution beneath the hot aqueous caustic alkali solution and withdrawing spent aqueous caustic alkali solution near the top 

1. A CONTINUOUS PROCESS FOR THE LEACHING OF AN IRON-ALUMINUM ALLOY, WHICH COMPRISES INTRODUCING FINELY COMMINUTED PARTICLES OF SAID ALLOY INTO AN AQUEOUS CAUSTIC ALKALI SOLUTION, MAINTAINING THE SOLUTION IN THE UPPER PART OF SAID COLUMN AT NEAR ITS BOILING TEMPERATURE DURING INTRODUCTION OF SAID ALLOY, INTRODUCING A COLD FRESH AQUEOUS CAUSTIC ALKALI SOLUTION NEAR THE BOTTOM OF SAID COLUMN, WITHDRAWING SPENT CAUSTIC ALKALI SOLUTION NEAR THE TOP OF SAID COLUMN, CONTROLLING THE INFLOW OF FRESH CAUSTIC ALKALI SOLUTION AT SUCH A RATE AS TO MAINTAIN THE LOWER PART OF SAID COLUMN RELATIVELY COOL WITH RESPECT TO THE UPPER PART OF SAID COLUMN BUT NOT AT A SUFFICIENTLY RAPID RATE TO CAUSE PARTICLES PRESENT IN SAID UPPER PART TO PASS OUT WITH THE SPENT CAUSTIC ALKALI SOLUTION AND INTERMITTENTLY RELEASING THE LEACHED PARTICLES FROM THE BOTTOM OF THE CAUSTIC ALKALI SOLUTION COLUMN INTO THE TOP OF AN UPWARDLY FLOWING COLUMN TO WASH WATER. 